Saturday, July 9, 2011

28 Jun 11: I cant help but thank the kind guys at Texas Instruments. I cant believe my eyes, they have shipped me a sample of their instrumentation amplifier. Thats would help me simplify my input block. Thanks u guys… You rock.

This project will describe building of a Pump control system. The requirement primarily arose to satiate the requirements of my parents, who have to manually switch on the pump every day morning and switch it off and continuously monitor the tank for overflow. So I have taken up the challenge onto myself...

However I would be ungrateful, I do not acknowledge the inputs I received after reading Kayne Richens blog post.

This blog is progressive ; hence will get updated as things progress.....

Lets me see how do things unfold...

Basic Design Objectives:-

Should be cheap and affordable.

Should be as automated as possible requiring minimal user supervision.

Should have a user-friendly MMI.

Prevent water and electricity wastage.

Design Challenges:-

Erratic water supply timings.

Non scheduled Electrical Load shedding .

High head of water tank.

Intelligent control system.

Preliminary System Design:-

System Blocks Functions:-

Input Block:-

Input Description

Sensor Type

Micro-controller Input

Sense Tank Capacity

Differential Pressure Sensor

Analog

Sense Electricity Availability

Optocoupler

Digital/Interrupt

Sense Time

RTC

Digital

Sense Input Water Supply Availability

Differential Pressure Sensor

Analog

Output Block:-

Output Description

Transducer Type

Micro-controller Output

Motor On/Off

Solid State Relay

Digital

Valve Solenoid On/Off

Relay

Digital

Alarm

Buzzer

Analog

Mathematics for Selecting Differential Pressure Sensor:-

Why Differential Pressure Sensor?

A differential pressure sensor will eliminate variation in pressure due to changes in atmospheric pressure.

Amplifier Design Objective : The output span of the transducer must be matched to the input span of the ADC to achieve optimum performance.

Mathematics for Amplifier Design

Span and Offset Characteristics at 10v,15v & 5V Excitation Voltage. As sensor is ratio-metric the the values are scaled for.

MPX2100DP

Excitation Voltage

Min Span(mV)

Max Span

(mV)

Min. Offset

(mV)

Max Offset

(mV)

10V

38.5

40

-1

1

15V (scaled)

57.75

60

-1.5

1.5

5V (scaled)

19.25

20

-0.5

0.5

9V(scaled)

34.65

3.6

-0.9

0.9

MPX2010DP

Excitation Voltage

Min Span(mV)

Max Span

(mV)

Min. Offset

(mV)

Max Offset

(mV)

10V

24

26

-1

1

15V (scaled)

36

39

-1.5

1.5

5V (scaled)

12

13

-0.5

0.5

9V(scaled)

21.6

23.4

-0.9

0.9

Desired Amplified Span and Offset

Desired Offset= 0.5VDesired Span = 5V

Gain Range & Offset Calculation

Maximum Gain =Desired Span (V)

Sensor’s Minimum Span

Desired Span = 5V

Excitation Voltage

Maximum Gain (MPX2100DP)

Maximum Gain (MPX2010DP)

10V

=5/38.5 = 129.8 = 130

208

15V

=5/57.75 = 86.58 = 87

139

5V

=5/19.25 = 259.75 = 260

417

9V

=5/34.65=144.300=144

231

Since Texas Instruments was kind to ship me samples of their instrumentation amplifiers, I would be basing my calculations on same. There is no rocket science involved since the datasheet is fairly self explanatory and the instrumentation amplifier itself requires only one external component for gain adjustment.